We are studying changes in the regulation of breathing during exposure to high altitude, hypoxia, or acid-base disturbances in order to understand more fully the nature of mechanisms fundamental to control of breathing under all circumstances. One of our current areas of interest is the mechanism(s) through which progesterone alters ventilation. We are attempting to determine whether it works primarily on the brain directly, on the peripheral chemoreceptors directly, or on mechanisms which control the ionic environment of the brain directly, which would then secondarily adjust ventilation. Another of our areas of interest is obtaining more and better information about the ionic environment of brain cells during normal conditions, and during alterations in oxygenation and acid-base status. We are going to use microelectrodes which are specifically sensitive to potassium, ions and others which are specifically sensitive to hydrogen ions to measure the concentrations of these ions around the brain cells.